fix(backend-services): use sync Twilio API call in executor

[billguo99]

Fix did not work:
https://github.com/ntls-io/nautilus-wallet/pull/567/files

From https://www.twilio.com/blog/send-sms-fastapi-twilio:

The problem is that the Twilio helper library for Python does not support asynchronous applications. Since this library will be making network requests to Twilio servers, it will block the loop if used directly in the asynchronous function. To avoid this problem, we’ll encapsulate all the Twilio related work in a function that we’ll call send_sms(), and we’ll execute this function inside an [executor](https://docs.python.org/3/library/asyncio-eventloop.html#executing-code-in-thread-or-process-pools) to keep the async application running smoothly.

From https://www.twilio.com/blog/twilio-python-helper-library-async:
Using Solution #3 - Using a thread executor

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[codecov-commenter]

Codecov Report

Merging #568 (ae20671) into main (76f7244) will not change coverage.
The diff coverage is n/a.

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